Consumer Reports tests caffeine levels of energy drinks

Health concerns about energy drinks were heightened this week when the Food and Drug Administration announced an investigation into five deaths that may be linked to Monster Energy Drink.

While caffeine is one of the key ingredients in energy drinks it can be hard to tell how much they contain. Consumer Reports just conducted lab tests on dozens of the top-selling drinks.

Everyone from Tim Tebow to 50 Cent and Joan Rivers are advertising energy drinks. With their Facebook pages and Internet video campaigns, manufacturers specifically target young people. But experts at Consumer Reports say you have to be careful how much caffeine you drink.

Consumer Reports analyzed the caffeine content of 27 top-selling energy drinks, testing three samples each. Although some products list the amount of caffeine on the package, they're not required to. Consumer Reports found the numbers can be way off.

"Some of the energy drinks underestimated the amount of caffeine listed on the label by 20 percent or more," said Williams.

So how much caffeine do energy drinks contain? In laboratory tests, it varied widely.